Device and method for producing a rotationally symmetrical, hollow metallic workpiece

ABSTRACT

Methods for producing a rotationally symmetrical, hollow metallic workpiece may involve rotating a casting mould about a rotation axis and introducing a melt into the casting mould. The melt may be thrown towards an inner contour of the casting mould by centrifugal forces, and hollow bodies may be added to the melt. Furthermore, a device for producing a rotationally symmetrical, hollow metallic workpiece may include a casting mould that is rotatable about a rotation axis, a feeder device for introducing a melt into the casting mould such that the melt is thrown towards an inner contour of the casting mould by the effect of a centrifugal force, and a metering device for adding hollow bodies to the melt.

CROSS REFERENCE TO RELATED APPLICATION

This application is a non-provisional application claiming priority from German Patent Application No. DE 10 2015 116 520.1, filed Sep. 29, 2015, entitled “Vorrichtung and Verfahren zur Herstellung eines rotationssymmetrischen, hohlen, metallischen Werkstücks” or, as translated, “Device and Method for Producing a Rotationally Symmetrical, Hollow Metallic Workpiece,” which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to devices and methods for producing a rotationally symmetrical, hollow metallic workpiece by way of rotating a casting mould and introducing a melt into the casting mould.

BACKGROUND

Austrian Patent Publication No. AT 407 646 B discloses a centrifugal casting method and a corresponding device for producing a rotationally symmetrical, hollow metallic workpiece, wherein a casting mould is rotated about a rotation axis. A liquid metallic melt is introduced into the casting mould along with grains or particles of a metallic compound that influence the wear properties of the material that is produced. As a result of the rotation of the casting mould, centrifugal forces act on the melt and on the particles. The density of the particles can be chosen to determine whether they concentrate in the outer area or in the inner area of the rotating casting mould. It is thus possible to adapt the workpiece to the local wear conditions.

In centrifugal casting methods of this kind, the melt is compacted by centrifugal forces, such that a workpiece is obtained with relatively high density and only a few casting defects such as voids or pores. This means that the workpieces produced are of a weight that is too great for many applications, for example, in the manufacture of cars. Therefore, a need exists for reducedweight workpieces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an example device for producing a rotationally symmetrical, hollow metallic workpiece.

FIG. 2 is a schematic sectional view of another example device for producing a rotationally symmetrical, hollow metallic workpiece.

FIG. 3 is a schematic sectional view of an example workpiece obtained using one of the example methods disclosed herein.

FIG. 4 is a schematic sectional view of another example workpiece obtained using one of the example methods disclosed herein.

DETAILED DESCRIPTION

Although certain example methods and apparatuses have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. Moreover, those having ordinary skill in the art will understand that reciting “a” element or “an” element in the appended claims does not restrict those claims to articles, apparatuses, systems, methods, or the like having only one of that element.

That said, one example object of the present disclosure is to reduce the weight of manufactured workpieces. This object and others may be achieved by the devices and the methods disclosed herein for producing a rotationally symmetrical, hollow metallic workpieces. In one example, a method may comprise rotating a casting mould about a rotation axis and introducing a melt into the casting mould. The melt may be thrown towards an inner contour of the casting mould by a centrifugal force.

Further, hollow bodies may be added to the melt. The hollow bodies that are added to the melt may become incorporated as the melt solidifies. In this respect, a workpiece can be obtained with cavities formed by the hollow bodies. Because the hollow bodies have a lower density compared to the material of the melt, the weight of the workpiece is reduced.

The material of the hollow bodies, in particular the material of an outer skin of the hollow bodies, may have a higher melting point than the material of the melt. As a result, there is no need to fear fusion of the hollow bodies in the melt. The melting point of the hollow bodies, in particular of the outer skin of the hollow bodies, may be above 700° C. in some examples, above 1500° C. in other examples, and above 2000° C. in still further examples. The melt may be advantageously liquid and/or metallic. The material of the melt may be a steel. Alternatively or in addition, the material of the melt can include aluminum, titanium, zinc, copper, or magnesium.

In some examples, the hollow bodies may be designed as hollow spheres. The hollow spheres can have a diameter of below 5 mm in some examples, below 1 mm in other examples, and below 250 μm in still further examples.

It may be advantageous if the hollow bodies comprise an inorganic, in particular ceramic material. For instance, the hollow bodies can comprise aluminum oxide (Al₂O₃), zirconium dioxide (ZrO₂), silicon carbide (SiC), boron carbide (B₄C), silicon nitride (Si₃N₄), titanium boride (TiB₂), tungsten carbide (WC), titanium carbide (TiC), silicon dioxide (SiO₂), or some combination of these materials. Alternatively or in addition, the hollow bodies can comprise a metallic material such as, for example, iron or an iron alloy.

In some cases, it has proven advantageous if the hollow bodies are pre-heated before being added to the melt. By way of the pre-heating, the hollow bodies can be brought to an increased temperature at which the danger of the melt setting upon initial contact with the hollow bodies is reduced. The hollow bodies can be pre-heated, for instance, to a temperature above 900° C. in some examples, above 1000° C. in other examples, or above 1100° C. in still further examples.

According to some examples, the hollow bodies may be added to the melt, which has been introduced into the casting mould, only when the melt has at least partially solidified in the casting mould. The at least partial solidification of the melt inside the rotating casting mould can be brought about by the effect of the centrifugal force. Alternatively or in addition, the melt can be cooled, for example, by cooling the casting mould. The mobility of the hollow bodies decreases in the partially solidified melt such that it is possible to reduce the effect whereby the hollow bodies and the melt separate through the different centrifugal forces acting on them. In this respect, a migration of the hollow bodies towards the rotation axis of the casting mould or towards the rotation axis of the produced workpiece can be reduced.

In this connection, it may be advantageous if, after the addition of hollow bodies, additional melt is introduced into the casting mould. The additional melt may be thrown by the effect of the centrifugal force towards the melt that has already at least partially solidified on the inner contour of the casting mould. The introduction of the additional melt permits the production of a layered structure of the workpiece. In some cases, it is possible to adjust the distribution of the hollow bodies through the choice of the quantity of melt and/or hollow bodies. The additional melt may be added only when the melt first introduced has already completely solidified, such that movements of the hollow bodies inside the melt are no longer possible. In this respect, it is possible to produce a workpiece with a layered structure, wherein an edge area of the workpiece directed towards the rotation axis of the workpiece has few hollow bodies or, in particular, is free of hollow bodies. Moreover, the inner contour of the workpiece can be smooth, thereby improving weldability.

In some examples, after the introduction of the additional melt, further hollow bodies may be added as soon as the additional melt has at least partially solidified. By the addition of further hollow bodies, a concentration of the hollow bodies can be increased in the edge area of the workpiece directed towards the rotation axis of the workpiece. It is moreover possible to generate a porous inner contour of the workpiece.

In one example method, the casting mould may be rotated about a horizontal rotation axis. In another example, the casting mould may be rotated about a vertical rotation axis.

The example object mentioned above may also be achieved by devices for producing a rotationally symmetrical, hollow metallic workpiece. In some examples, a device may comprise a casting mould that is rotatable about a rotation axis, a feeder device for introducing a melt into the casting mould, and a metering device for adding hollow bodies to the melt that has been introduced into the casting mould.

The example devices disclosed herein permit the same advantages as those that have already been described in connection with the various example methods for producing a rotationally symmetrical, hollow metallic workpiece.

With reference now to the figures, further details, features, and advantages of the present disclosure will become clear from the figures and from the following description with reference to the figures. It should be understood that the figures only depict illustrative examples and do not in any way limit the scope of the present disclosure. Moreover, identical parts are typically provided with like reference signs in the various figures, for which reason said parts are each generally mentioned only once.

FIG. 1 shows an example device 1 for centrifugal casting for producing a rotationally symmetrical, hollow metallic workpiece. The example device 1 comprises an example casting mould 2, also referred to as a permanent mould, which is shown in this example to be mounted about a vertical rotation axis V. The casting mould 2 has a cover 3 with an admission opening through which a liquid metallic melt 4 can be introduced into the casting mould 2. Moreover, the device 1 comprises an example feeder device 12 for introducing the melt 4 into the casting mould 2, which feeder device 12 comprises an example casting crucible 5. During the rotation of the casting mould 2, the melt 4 introduced into the casting mould 2 may be thrown towards an inner contour 8 of the casting mould 2 by centrifugal forces. The centrifugal forces may compact the melt 4 on the inner contour 8 and contribute to the melt 4 at least partially solidifying. During the compaction of the melt 4, undesired air inclusions may be expelled such that the formation of shrink holes and undesired pores is counteracted.

In some cases, the material of the melt 4 may be steel. In alternative examples or in addition, the material of the melt 4 can include aluminum, titanium, zinc, copper, or magnesium.

In some examples, the device 1 may comprise a metering device 7 for adding hollow bodies 6 to the melt 4 introduced into the casting mould 2. The hollow bodies 6 may be incorporated into the melt 4 as the latter solidifies and form cavities in the generated workpiece 11. In this respect, a workpiece 11 with desired and defined cavities can be obtained using the device 1, wherein the cavities reduce the weight of the workpiece 11. The hollow bodies 6 may be designed as hollow spheres. The diameter of the hollow spheres may be in a range of below 5 mm in some examples, below 1 mm in other examples, or below 250 μm in still other examples. Hollow bodies 6 made of a ceramic material may be used, as a result of which the stiffness and/or the wear properties of the workpiece 11 can be improved. For example, the hollow bodies 6 can comprise aluminum oxide (Al₂O₃), zirconium dioxide (ZrO₂), silicon carbide (SiC), boron carbide (B₄C), silicon nitride (Si₃N₄), titanium boride (TiB₂), tungsten carbide (WC), titanium carbide (TiC), or silicon dioxide (SiO₂). Alternatively or in addition, the hollow bodies can comprise a metallic material such as, for example, iron or an iron alloy.

The example production device 1 may further comprise a pre-heating mechanism by which the hollow bodies 6 can be pre-heated, thereby reducing any danger of undesired setting of the melt 4 upon introduction of the hollow bodies 6 into the casting mould 2. The pre-heating means can, for example, be arranged in the metering device 7 and/or can heat the metering device 7. The hollow bodies 6 may be pre-heated to a temperature of above 900° C. in some examples, above 1000° C. in other examples, or above 1100° C. in still further examples.

FIG. 2 shows another example device 1 for centrifugal casting for producing rotationally symmetrical, hollow metallic workpieces 11. In contrast to the device shown in FIG. 1, the casting mould 2 in the example device 1 shown in FIG. 2 is arranged to be rotatable about a horizontal rotation axis H. Moreover, the casting mould 2 is mounted on several roller bearings 10.

The feeder device 12 may have, in addition to the casting crucible 5, a casting channel 9 that is arranged in such a way that it passes through a recess in a side cover 3 of the casting mould 2. By way of the casting channel 9, the melt 4 can be introduced into the casting mould 2. Moreover, the metering device 7 for adding the hollow bodies 6 may be arranged in such a way that the hollow bodies 6 can be added to the melt 4 in the casting channel 9. In this respect, a mixture of the melt 4 and the hollow bodies 6 can be introduced jointly into the casting mould 2. Alternatively, it is possible to introduce exclusively the melt 4 or exclusively the hollow bodies 6 into the casting mould 2 via the casting channel 9.

With the example devices described above and shown in FIGS. 1 and 2, various methods can be carried out in which the casting mould 2 may be rotated and a melt 4 may be introduced into the rotating casting mould 2. The melt 4 may be thrown towards the inner contour 8 of the casting mould 2 by the effect of a centrifugal force. Moreover, hollow bodies 6 may be added to the melt 4 in order to reduce the weight of the workpiece 11.

In some examples, the melt 4 and the hollow bodies 6 can be added simultaneously to the casting mould 2. However, in other examples, the melt 4 and the hollow bodies 6 may be added sequentially, as a result of which it is possible to generate a layered structure of the workpiece 11. Example methods resulting in such a layered structure of the workpiece 11 are described below.

In a first step of some example methods, the melt 4 may be exclusively added to the casting mould 2. The melt 4 may be thrown outwards and may partially solidify on the inner contour 8 of the casting mould 2. In a second step of some example methods, the hollow bodies 6 may be added such that the hollow bodies 6 are at least partially enclosed by the melt 4. The mobility of the hollow bodies 6 is reduced in the partially solidified melt 4, and therefore undesired movements of the hollow bodies 6 in the direction of the rotation axis H, V of the casting mould 2 are reduced.

In a third step of some example methods, after hollow bodies 6 have been added, additional melt 4 may be introduced into the casting mould 2. The additional melt 4 introduced in this step may likewise be thrown, by the effect of the centrifugal force, towards the melt 4 that has already partially solidified on the inner contour 8 of the casting mould 2. In some examples, the additional melt 4 may be added only when the melt 4 first introduced has already completely solidified, such that movements of the hollow bodies 6 inside the melt 4 are no longer possible. In this way, a workpiece 11 with a layered structure can be produced in which an edge area of the workpiece 11 directed towards the rotation axis of the workpiece 11 has few hollow bodies or, in particular, is free of hollow bodies.

In a fourth step used in some example methods, further hollow bodies 6 may be added after the introduction of the additional melt 4. If hollow bodies 6 are added last of all in such methods, it is possible to produce a hollow, rotationally symmetrical workpiece 11 with a porous inner contour.

FIG. 3 shows one example rotationally symmetrical, hollow metallic workpiece 11 produced by one of the methods according to the present disclosure. The example workpiece 11 has a layered structure. The outer surface of the workpiece 11 and the inner surface of the workpiece may be smooth, which can be achieved by the fact that the edge areas 12, 13 of the workpiece that are directed towards the outer surface and the inner surface may have few hollow bodies or, in some cases, may be free of hollow bodies. In an inner area 14 lying to the inside of the workpiece 11, there may be an increased concentration of hollow bodies 6.

FIG. 4 shows another example rotationally symmetrical, hollow metallic workpiece 11 produced by one of the methods according to the present disclosure. This example workpiece 11 has a layered structure. The outer surface of the workpiece 11 and the inner surface of the workpiece may be smooth, which can be achieved by the fact that the edge areas 12, 13 of the workpiece that are directed towards the outer surface and the inner surface may have few hollow bodies or, in some cases, may be free of hollow bodies. In an inner area 14 lying to the inside of the workpiece 11, there may be an increased concentration of hollow bodies 6. Portions 15 with a high concentration of hollow bodies 6 and portions 16 with a low concentration of hollow bodies 6 can be provided in the inner area 14. To produce the portions 15 with a high concentration of hollow bodies 6 and the portions 16 with a low concentration of hollow bodies 6, the hollow bodies 6 may be added sequentially during the example methods described above.

The production of the example workpiece 11 shown in FIG. 4 can take place, for example, in the example device 1 shown in FIG. 2. The casting channel 9 of the device 1 can be linearly movable in a direction parallel to the rotation axis H. During the introduction of the melt 4 into the casting mould 2, the casting channel 9 can be moved parallel to the rotation axis H. Hollow bodies 6 can be added to the melt 4 in order to generate portions 15 with a high density of hollow bodies. The addition of the hollow bodies 6 to the melt 4 can be interrupted in order to obtain portions 16 with a low density of hollow bodies. 

What is claimed is:
 1. A method for producing a rotationally symmetrical, hollow metallic workpiece, the method comprising: rotating a casting mould about a rotation axis; introducing a melt into the casting mould, wherein the melt is thrown towards an inner contour of the casting mould by centrifugal forces; and adding hollow bodies to the melt.
 2. The method of claim 1 wherein a material of the hollow bodies has a higher melting point than a material of the melt.
 3. The method of claim 1 wherein the hollow bodies are configured as hollow spheres.
 4. The method of claim 1 wherein the hollow bodies comprise a ceramic material.
 5. The method of claim 1 wherein the hollow bodies comprise aluminum oxide, zirconium dioxide, silicon carbide, boron carbide, silicon nitride, titanium boride, tungsten carbide, titanium carbide, or silicone dioxide.
 6. The method of claim 1 wherein the hollow bodies comprise a metallic material.
 7. The method of claim 1 wherein the hollow bodies comprise iron or an iron alloy.
 8. The method of claim 1 wherein the hollow bodies comprise a ceramic material, aluminum oxide, zirconium dioxide, silicon carbide, boron carbide, silicon nitride, titanium boride, tungsten carbide, titanium carbide, silicone dioxide, a metallic material, iron, an iron alloy, or some combination thereof.
 9. The method of claim 1 further comprising preheating the hollow bodies prior to adding the hollow bodies to the melt.
 10. The method of claim 1 wherein the hollow bodies are added to the melt in the casting mould after the melt has at least partially solidified in the casting mould.
 11. The method of claim 1 wherein the melt is a first melt, the method further comprising introducing a second melt into the casting mould after the addition of the hollow bodies, wherein the second melt is thrown by centrifugal forces towards the first melt that has already at least partially solidified on the inner contour of the casting mould.
 12. The method of claim 7 further comprising adding additional hollow bodies after introducing the second melt and after the second melt has at least partially solidified.
 13. The method of claim 1 wherein the rotation axis about which the casting mould is rotated is a horizontal rotation axis.
 14. The method of claim 1 wherein the rotation axis about which the casting mould is rotated is a vertical rotation axis.
 15. The rotationally symmetrical, hollow metallic workpiece produced from the method of claim
 1. 16. A device for producing a rotationally symmetrical, hollow metallic workpiece, the device comprising: a casting mould that is rotatable about a rotation axis; a feeder device for introducing a melt into the casting mould; and a metering device for adding hollow bodies to the melt. 